Understanding geology, weather, climate, and the planet we live on.
Why Earth Science Matters
This knowledge helps you:
- Understand natural disasters and hazards
- Make sense of climate change discussions
- Appreciate geological time and Earth's history
- Prepare for weather events
- Understand where resources come from
- Evaluate environmental claims
Earth's Structure
Layers of the Earth
| Layer | Depth | Composition | State |
|---|
| Crust | 0-70 km | Rock (continental: granite, oceanic: basalt) | Solid |
| Upper mantle | 70-400 km | Silicate rock | Mostly solid, flows slowly (asthenosphere) |
| Lower mantle | 400-2,900 km | Denser silicates | Solid (but flows slowly) |
| Outer core | 2,900-5,150 km | Iron and nickel | Liquid |
| Inner core | 5,150-6,370 km | Iron and nickel | Solid |
Key Facts
| Fact | Detail |
|---|
| Earth's age | 4.5 billion years |
| Surface area | 510 million km2 |
| Water coverage | 71% of surface |
| Deepest ocean point | Mariana Trench (11 km) |
| Tallest mountain | Everest (8.8 km above sea level) |
Plate Tectonics
The Basic Idea
Earth's crust is broken into plates that move on the mantle.
| Evidence | What It Shows |
|---|
| Continent shapes | Africa and South America fit together |
| Fossil distribution | Same fossils on different continents |
| Rock matching | Same rock formations across oceans |
| Seafloor spreading | New crust forms at mid-ocean ridges |
Plate Boundaries
| Type | What Happens | Features Created |
|---|
| Divergent | Plates move apart | Mid-ocean ridges, rift valleys |
| Convergent | Plates collide | Mountains, trenches, volcanoes |
| Transform | Plates slide past each other | Fault lines |
Geological Features
| Feature | How It Forms |
|---|
| Mountains | Plates collide, crust crumples upward |
| Volcanoes | Magma rises through crust |
| Earthquakes | Stress releases at plate boundaries |
| Ocean trenches | One plate subducts under another |
| Rift valleys | Plates pull apart on land |
Earthquake Basics
| Term | Definition |
|---|
| Epicenter | Point on surface above where quake originates |
| Focus | Actual location underground where quake starts |
| Magnitude | Energy released (Richter/moment magnitude scale) |
| Intensity | Shaking felt at a location (Modified Mercalli) |
Magnitude scale:
| Magnitude | Effects |
|---|
| < 3.0 | Usually not felt |
| 3.0-3.9 | Felt, rarely causes damage |
| 4.0-4.9 | Noticeable shaking, minor damage |
| 5.0-5.9 | Can cause significant damage |
| 6.0-6.9 | Strong, destructive in populated areas |
| 7.0+ | Major destruction possible |
Volcanic Activity
| Volcano Type | Characteristics | Example |
|---|
| Shield | Broad, gentle slopes, fluid lava | Hawaii |
| Stratovolcano | Steep, explosive | Mt. St. Helens |
| Cinder cone | Small, steep, short-lived | Paricutin |
The Rock Cycle
Three Rock Types
| Type | Formation | Examples |
|---|
| Igneous | Cooled from molten rock | Granite, basalt, obsidian |
| Sedimentary | Accumulated and compressed sediments | Sandstone, limestone, shale |
| Metamorphic | Changed by heat and pressure | Marble, slate, quartzite |
The Cycle
Igneous → (weathering) → Sediments → (compaction) → Sedimentary
↑ ↓
← (melting) ← Metamorphic ← (heat/pressure) ←─────────┘
All rock types can transform into any other given enough time and the right conditions.
Weathering and Erosion
| Process | Description | Example |
|---|
| Mechanical weathering | Physical breakdown | Frost cracking rock |
| Chemical weathering | Chemical breakdown | Acid rain dissolving limestone |
| Erosion | Transport of material | River carrying sediment |
| Deposition | Material settles | River delta forming |
The Atmosphere
Composition
| Gas | Percentage | Role |
|---|
| Nitrogen | 78% | Inert, dilutes oxygen |
| Oxygen | 21% | Respiration, combustion |
| Argon | 0.9% | Inert |
| Carbon dioxide | 0.04% | Greenhouse gas, photosynthesis |
| Water vapor | Variable | Weather, greenhouse effect |
Atmospheric Layers
| Layer | Altitude | Characteristics |
|---|
| Troposphere | 0-12 km | Weather occurs here |
| Stratosphere | 12-50 km | Contains ozone layer |
| Mesosphere | 50-80 km | Meteors burn up |
| Thermosphere | 80-700 km | Aurora occurs |
| Exosphere | 700+ km | Fades into space |
Weather
Weather vs. Climate
| Weather | Climate |
|---|
| Day-to-day conditions | Long-term average conditions |
| Changes rapidly | Changes slowly |
| Specific time and place | Regional patterns over decades |
| "What's it like today?" | "What's it usually like here?" |
Key Weather Concepts
| Concept | Explanation |
|---|
| Air pressure | Weight of air above; high = fair, low = storms |
| Humidity | Water vapor in air |
| Front | Boundary between air masses |
| Precipitation | Water falling from atmosphere |
Types of Fronts
| Front Type | What Happens | Weather |
|---|
| Cold front | Cold air pushes under warm | Storms, then clearing |
| Warm front | Warm air rises over cold | Extended rain, then warming |
| Stationary | Neither moves | Prolonged clouds and rain |
| Occluded | Cold catches warm | Complex, variable weather |
Severe Weather
| Type | Conditions | Safety |
|---|
| Thunderstorm | Unstable air, moisture | Stay indoors, away from windows |
| Tornado | Rotating thunderstorm | Lowest floor, interior room |
| Hurricane | Warm ocean, low pressure | Evacuate if ordered, shelter |
| Flash flood | Heavy rain, poor drainage | Never drive through floods |
Reading Weather Forecasts
| Term | Meaning |
|---|
| 30% chance of rain | 30% probability of measurable rain at any point |
| Wind chill | How cold it feels with wind |
| Heat index | How hot it feels with humidity |
| Dew point | Temperature at which condensation occurs |
Climate
Climate Zones
| Zone | Characteristics | Location |
|---|
| Tropical | Hot, wet year-round | Near equator |
| Dry | Little precipitation | Deserts, interior regions |
| Temperate | Moderate, seasonal | Mid-latitudes |
| Continental | Extreme seasons | Interior continents |
| Polar | Cold year-round | Near poles |
What Determines Climate
| Factor | Effect |
|---|
| Latitude | Distance from equator affects temperature |
| Altitude | Higher = cooler |
| Ocean currents | Moderate coastal temperatures |
| Mountains | Block weather patterns, create rain shadows |
| Distance from water | Coastal vs. continental climate |
Climate Change
The Greenhouse Effect
| Step | What Happens |
|---|
| 1 | Sun's energy reaches Earth |
| 2 | Earth absorbs energy, warms up |
| 3 | Earth radiates heat (infrared) |
| 4 | Greenhouse gases trap some heat |
| 5 | Heat retained, planet stays warm |
Without greenhouse effect: Earth would average -18C (0F) instead of 15C (59F).
Climate Change Evidence
| Evidence | What It Shows |
|---|
| Temperature records | Global average rising |
| Ice cores | CO2 levels highest in 800,000 years |
| Sea level rise | Oceans expanding, ice melting |
| Glacier retreat | Ice sheets shrinking |
| Ocean acidification | CO2 absorbed by oceans |
| Species migration | Animals moving to new ranges |
Human Impact
| Cause | Contribution |
|---|
| Fossil fuels | 65% of greenhouse emissions |
| Deforestation | 11% of emissions |
| Agriculture | 12% of emissions |
| Industry | 12% of emissions |
Observed and Projected Changes
| Change | Already Happening | Projected |
|---|
| Temperature | +1.1C since pre-industrial | +1.5-4.5C by 2100 |
| Sea level | +20 cm since 1900 | +30-110 cm by 2100 |
| Extreme weather | More frequent | Further increase |
| Arctic ice | 40% less summer ice | Possible ice-free summers |
Water Cycle
The Process
| Stage | What Happens |
|---|
| Evaporation | Water becomes vapor |
| Transpiration | Plants release water vapor |
| Condensation | Vapor forms clouds |
| Precipitation | Water falls as rain, snow, etc. |
| Collection | Water gathers in oceans, lakes, groundwater |
| Runoff | Water flows to bodies of water |
Groundwater
| Concept | Definition |
|---|
| Water table | Top of saturated zone underground |
| Aquifer | Underground layer that holds water |
| Recharge | Water entering aquifer |
| Overdraw | Using water faster than recharge |
Earth's Resources
Types of Resources
| Category | Examples | Renewable? |
|---|
| Fossil fuels | Coal, oil, natural gas | No (millions of years) |
| Minerals | Iron, copper, rare earths | No (geological timescales) |
| Soil | Topsoil for agriculture | Slowly (centuries) |
| Fresh water | Rivers, aquifers | Yes (with proper management) |
| Timber | Forests | Yes (decades) |
Resource Concerns
| Issue | Problem |
|---|
| Fossil fuel depletion | Finite supply, emissions |
| Aquifer depletion | Overuse, slow recharge |
| Soil erosion | Poor practices, deforestation |
| Mineral scarcity | Concentrated in few locations |
Key Takeaways
Earth is dynamic - Plates move, mountains rise, rocks cycle over millions of years
Plate tectonics explains major features - Mountains, earthquakes, and volcanoes result from plate movement
Weather and climate are different - Weather is short-term; climate is long-term average
The greenhouse effect is natural - But enhanced by human activities
Climate change is measurable - Temperature, ice, sea level all show consistent changes
Water cycles continuously - Evaporation, precipitation, collection
Resources are finite - Many take geological timescales to form
Natural hazards are predictable - Not individually, but risk zones are known
Earth's history is immensely long - 4.5 billion years; humans are very recent
Understanding Earth helps you prepare - For weather events, natural disasters, and environmental changes